Nokia Power User spied that Microsoft's upcoming Windows Phone 8.1 update crossed yet another certification hurdle, this time for Bluetooth 4.0. The Bluetooth specification is already supported on competing iOS and Android devices.

According to the listing on the Bluetooth Special Interest Group (BSIG) website, Microsoft received Bluetooth 4.0 certification for Windows Phone 8.1 on January 31, more than five months after submitting the mobile OS on August 5, 2013.

The BSIG certification page twice specifically includes mention of Bluetooth Low Energy (LE) support, a feature that has been widely expected given the increasing popularity of devices coupled to mobile apps that support the technology.

Great, but when?

When the update might start landing on user handsets is anyone's guess, but with Microsoft's annual Build developer conference kicking off April 2 in San Francisco, we wouldn't be surprised to see at least a preview version land in the hands of devs during the event.

Previous sources claimed that Windows Phone 8.1 will be released to manufacturers next month, with a final release to end users arriving sometime in May.

It's important to note Microsoft's BSIG listing only covers the "mobile phone operating system" itself, although Nokia has already confirmed Bluetooth 4.0 support for its Lumia line, and all Windows Phone 8 devices are expected to be eligible for the update to 8.1.

Relive the excitement of Windows 8.1 all over again in our full review!